Alarm circuit for indicating failure in redundant power supplies

ABSTRACT

The output voltages of a pair of dual polarity power supplies are coupled together through associated solid state alarm-sense circuits to common utilization equipment. Each alarm-sense circuit comprises a pair of switching transistors connected to associated voltage dividers that are connected across the output lines of a power supply; a pair of transistors connected in parallel; and a lamp. The output lines supporting the same polarity voltages are connected together through steering diodes that prevent one supply loading the other. The switching transistors detect increases and decreases in supply voltages that are greater than prescribed amounts. In each alarm-sense circuit, the parallel connected transistors are responsive to the operation of the switching transistors to light the lamp to indicate failure of the associated power supply. Output signals of the alarm-sense circuits are connected to a bell for also producing an audio alarm when a power supply fails. A zener diode is connected to a voltage divider for causing a switching transistor to detect a supply failure when the absolute values of the opposite polarity supply voltages from an associated power supply increase at the same rate.

United States Patent Golja Nov. 7, 1972 [54] ALARM CIRCUIT FORINDICATING FAILURE IN REDUNDANT POWER SUPPLIES [72] Inventor: JosephGolin, Redwood City, Calif.

73} Assignee: GTE Automatic Electric Laboratories, Incorporated,Northlake, ill.

22 Filed: Sept. 3, 1911 211 Appl.No.: 177,765

52] us. 01.... ..34o/24a A, 340/333 51 im. Cl ..-F08b 21/00 [58] Fieldof Search ..340/24s A, 248 R, 411

[56] References Cited UNITED STATES PATENTS- 3,431,557 3/1969 Thomas.,..340/248 A Primary Examiner-Thomas B. Habecker IAttorney-K.,Mullerheim et al. and Theodore C. Jay, Jr.

The output voltages of a pair of dual polarity power supplies arecoupled together through associated solid state alarm-sense circuits tocommon utilization equipment. Each alarm-sense circuit comprises, a pairof switching transistors connected to associated voltage dividers thatare connected across the output lines of a power supply; a pair oftransistorsconnected in parallel; and a lamp. The output linessupporting the same polarity voltages are connected together through Isteering diodes that prevent one supply loading the to detect a supplyfailure when the absolute values of the opposite polarity supplyvoltages from an associated power supply increase at the same rate.

[57] ABSTRACT 7 Claims, 3 Drawing Figures -|2v +|2v| |9 I0 TOUTILIZATION |,8

6 4o APPARATUS .L .1- a +|3v A r- T 2e 30 is I 47 BELL I CIRCUIT 43 i rl l I 26 Q5 l 59 3| l a I 1 I l I 52 55 2| 63 35' 4|A' I l 9 I 29 I |3v5s 56 l l, E I I? 7 4| 7 l5 awn-4 1 ALARM CIRCUIT FOR INDICATING FAILUREIN REDUNDANT POWERSUPPLIES BACKGROUND OF INVENTION This inventionrelates to alarm circuits and more par ticularly toalarm circuits formonitoring the operation of and indicating failure of redundant powersupplies.

In certain applications it is desirable to insure that a system does notbecome inoperative as a result of lack of electrical power. In suchsystems an inoperative standby power supply cannot be used since thesystem would be inoperative from the time the supply failure is detectedto the'time the auxiliary supply is energized and connected in thesystem. Redundant power supplies are employed in such applicationswherein a'pair of power supplies that are both on are connected to acommon load with the power supply having the higher voltage supplyingcurrent to the load. in the prior art, monitor circuits associated withthe power supplies employ relays as sense and control elements forproducing an alarm indicating failure of a particular supply so that itcan be repaired before the system becomes inoperative. Relays arerelatively large and expensive and have poor sensitivity in that theysense catastrophic failure of a power supply rather than relativelysmall changes in the output voltage thereof.

An object of this invention is the provision of an improved alarmcircuit for monitoring the operationof redundant power supplies.

Another object is the provision of an alarm circuit that is physicallysmall and inexpensive and senses small changes in the output voltage ofa power supply.

- DESCRIPTION OF DRAWING This invention will be more fully understoodfrom the following detailed description thereof together with thedrawing in which:

FIG. 1 is a block diagram illustrating connection of equipment embodyingthis invention to redundant power supplies;

FIG. 2 is a circuit diagram of one embodiment of this invention; and

FIG. 3 is a circuit diagram of an alternate embodiment of thisinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1 redundantpower supplies 4 and 5 each produce constant DC output voltages of :13V, for example, on lines 6, 7 and 8, 9, respectively. These outputvoltages of supplies 4 and 5 are connected through associatedalarm-sense circuits 10 and 11 and lines 14, 15 and 16, 17,respectively, to audio alarm apparatus 18. The output voltages of thepower supplies are combined and applied on lines 19 and 20 toutilization apparatus (not shown). The power supplies and alarm-sensecircuits are each connected toa common ground reference potential.Outputs of alarmsense circuits 10 and 11 are also applied on associatedlines 21 and 22 to the audio alarm apparatus for controlling operationof the latter.

Referring now to FIG. 2, audio alarm apparatus 18 comprises a bellcircuit 26, and a relay 27 having a coil 28 connected in series with acurrent limiting resistor 29 across the outputs of the power supplies.One side of the bell circuit 26 is connected on line- 30 to the positivesupply voltage lines 14 and 16. The other side of circuit 26 isconnected on line 31 to the movable arm of the relay. When at least onepower supply is operating, coil 28 is energized and arm 32 is connectedto the relay contact point 33 which is floating. When coil 28 isde-energized, arm 32 is connected to relay contactpoint 34 which isconnected through line 35 to the negative supply voltage to ring thebell.

Since'alarrmsense circuits l0 and 11 are identical, only circuit 10 willbe described in detail in relation to thecircuit diagrams in FIGS. 2 and3 where similar components are designated by the same referencecharacters. Again referring toFIG. 2, the circuit 10 comprises steeringdiodes 40 and 41, zener diode 43, switching transistors Q and 0,,transistors Q, and O, which are connected in parallel, lamp 46, andswitching transistor 0;. Steering diodes 40 and 41 (and also diodes 40Aand 41A of circuit 11) are connected in series with the positive andnegative, respectively, output voltagelines of the power supplies. Thesteering diodes are employed to couple the output voltages of the twopower supplies together and to lines 14-17, and to isolate the powersupplies from each other. Thus, if one supply fails it will not load theinternal circuitry of and affect operation of the other power supply.The power supply with the largest absolute value of output voltage willconduct through the associated steering diode and supply current to theutilization apparatus. The voltages on lines 19 and 20 are lower thanil3V output voltages from the supplies by the diode voltage drops.

The Q, and Q, collector electrodes are connected through associatedresistors 47 and 48 to the positive supply voltage line 14 where theycan receive voltage from either power supply. A resistor 49 is connectedbetween the Q collector and emitter electrodes, the

former electrode being connected to the 0 base electrode for controllingoperation of Q, and the latter electrode being connected to ground asare the Q and Q emitter electrodes.

A pair of voltage dividers comprising resistors 52, 53 and 54, 55 areconnected in shunt across the output 'voltage lines 6 and 7 of powersupply 4. The voltage dividers are isolated from the output voltages ofthe other supply 5 by steering diodes 40 and 41. Zener diode 43 isconnected in parallel with resistor 54. The Q, and Q, base electrodesare connected through current limiting resistors 56 and 57 to thejunctions 58 and 59, respectively, of the voltage dividers which bias Q,on and Q, off. The Q, emitter electrode is connected to the 0; baseelectrode to'control operation of the latter transistor.

Lamp 46 and collector resistor 60 are connected in series between the Qand Q collector electrodes and the positive supply voltage on line 14.The'Q, base electrode is connected through resistor 61 to the collectorsof Q: nd Q The O emitter electrode is connected on line'62 to thepositive supply voltage line 14. The Q, collector electrode is connectedthrough output line 21 to junction 63 so that 0 is essentially inparallel with the relay coil 28.

In operation, O is saturated and the other transistors are cut off whenthe :13V output voltages of power supply 4 vary less than 10 percent.The operation of Q and Q, is controlled by the bias potential atthejunctions 58 and 59 of the voltage dividers. The bias levels at which0, and Q, change conduction states is a function of the base-emitterdrops of these transistors and Q, and the values of resistors 56 and 57.Thus, these bias levels may not be symmetrical, i.e., both may not bedifferent from the supply voltage by the same amount.

Consider that power supply 4 fails by either +l3V going less positive bymore than 1.3V, or l3V going more negative by more than l.3V, or both.This causes the potential at junction 58 to become more negative thanthe sum of the base-emitter drop of Q and the voltage across resistor56, and to cut off transistor 0,. The resultant increase in the Qcollector voltage saturates 0, to light lamp 46 to indicate that powersupply 4 has failed. The decrease in Q collector voltage causes 0,, toconduct to short circuit and de-energize coil 28 to connect circuit 26to the 1 3V lines l5, l7 and ring the bell. In a similar manner, ifpower supply 4 fails by either +l3V becoming more positive by more thanl.3V, or l3V becoming less negative by more than l.3V, or both, Q: iscaused to conduct by the potential at junction 59. This causes toconduct to light the lamp, saturate Q and ring the bell.

If the :13V output voltages of supply 4 both increase in absolute value(i.e., +l3V goes more positive and 1 3V goes more negative) at the samerate, the voltage at junction 59 remains essentially constant. Thus, Qtends to remain cut off although the supply potential has changed morethan the prescribed amount. When the potential across resistor 54reaches the zener breakdown voltage, however, diode 43 conducts to raisethe junction 59 potential to drive Q into conduction. This causes Q andQ; to also conduct to light lamp 46 and ring the bell in circuit 26.

In the alternate embodiment of the invention illustrated in FIG. 3, theswitching transistor is omitted from alarm circuit and a relay coil 67is connected in serieswith lamp 46 and the collectors of Q, and Q Therelay contact point 68 is connected to the l3V line 15 instead of thefloating contact point 69 as in FIG. 2. The arm 70 of the relay isconnected on line 21 to bell circuit 26 of the audio alarm apparatus.Thus, in contrast to the operation of the relay in FIG. 2, relay coil 67is de-energized during normal operation and is energized, duringconduction of Q or Q, by collector current thereof to ring the bell ofcircuit 26.

What is claimed is:

circuits" for producing common output voltages of opposite p larit'y; Ieach of said alarm circuits comprising lines of a difierent associatedpower supply;

5s 1. Apparatus for indicating failure of redundant.

. a-first transistor of one type having a collector electrode receivingthe output voltages of one polarity from the power. supplies, having anemitter electrode connected to a ground.

reference potential and having a base electrode;

first bias meansconnected across the output lines In of the associatedpower supply and to said first transistorbaseelectrode for biasing saidfirst transistor on during quiescent conditions when I the powersupplies operate satisfactorily;

second bias means connected across the output lines of the associatedpower supply;

alamp; and r second and third transistors of the one type having emitterelectrodes connected to the ground reference potential; havingbaseelectrodes electrically connected to the first transistor collectorelectrode and to said second bias means, respectively, for biasing said'second and third transistors ofi during quiescent conditions; and havingcollector electrodes connected in series through said lamp to receivethe one polarity voltages from the power supplies;

said first transistor being cut off and causing conduction of saidsecond transistor and illumination of said lamp for indicating failureof the. associated power supply when eitherthe relative magnitude of theone polarity voltage, or the relative magnitude of the other polarityvoltage, or both therefrom change in one direction an amount greaterthan a prescribed limit;

said third transistor conducting and causing illumination of said lampfor indicating failure of the associated power supply when either therelative magnitude of the one polarity voltage,

. or the relative magnitude of the other polarity voltage, or boththerefrom change in the other direction an amount greater than aprescribed limit.

2.' Apparatus according to claim 1 wherein each alarm circuit includes apair of steering diodes, each diode being connected in series with adifferent output line of the associated power supply, said first, secondand third transistor collector electrodesv being connected to the oneside of one diode that is spaced from the one output line supplying theone polarity voltage.

3. Apparatus according to claim 2 including means responsive to currentin the common collector circuits of said second and third transistorsfor producing an audio indication of failure of a power supply.

4. Apparatus according to claim 3 wherein said second bias meanscomprises a resistive voltage divider connected across the supply outputlines and a fourth transistor of the one type'having a collectorelectrode electrically connected to the one side of the one diode,having a base electrode electrically connected to the voltage divider,and having an emitter electrode electrically connected to the baseelectrode of said third transistor, said fourth transistor being cut offduring quiescent operation and conducting for causing said thirdtransistor to conduct to illuminate said lamp to indicate failure of theassociated power supply when eitherthe relative magnitude of the onepolarity voltage,- or the relative magnitude of the other polarityvoltage, or both therefrom change in the other direction an amountgreater than a prescribed limit.

5. Apparatus according to claim 4 wherein said second bias meansincludes a zener diode electrically connected between-said fourthtransistor base electrode andthe output line supporting the one polarityvoltage from the associated supply for causing conduction of thistransistor when the opposite polarity voltages therefrom each increasein absolute value more than a prescribed amount at the same rate.

6. Apparatus according to claim 5 wherein each alarm circuit comprises arelay including a coil connected in series with said second and thirdtransistor collector electrodes and said lamp, and said audio indicationproducing means comprises an audio device responsive to operation ofsaid relay for producing an audio indication of failure of a powersupply.

[Apparatus according to claim 5 wherein said audio indication producingmeans comprises an audio device and a relay electrically connected tothe sides of said steering diodes away from the supplies and to saidaudio device, said relay being normally energized to deactivate saidaudio device; and wherein said alarm circuits each comprise a fifthtransistor of the opposite conduction type electrically connected acrosssaid relay and to said second and third transistor collector electrodes,said fifth transistor being responsive to conduction of either of saidsecond and third transistors for conducting to short circuit anddeenergize said relay to activate said audio device to produce an audioindication of failure of a power supply.

# l l l 1F

1. Apparatus for indicating failure of redundant power supplies thatincludes a pair of DC power supplies, each supply having a pair ofoutput lines supplying output voltages of opposite polarity, comprisinga pair of alarm circuits; means for connecting each alarm circuit acrossthe output lines of a different associated power supply; and means forcombining output signals from said alarm circuits for producing commonoutput voltages of opposite polarity; each of said alarm circuitscomprising a first transistor of one type having a collector electrodereceiving the output voltages of one polarity frOm the power supplies,having an emitter electrode connected to a ground reference potentialand having a base electrode; first bias means connected across theoutput lines of the associated power supply and to said first transistorbase electrode for biasing said first transistor on during quiescentconditions when the power supplies operate satisfactorily; second biasmeans connected across the output lines of the associated power supply;a lamp; and second and third transistors of the one type having emitterelectrodes connected to the ground reference potential; having baseelectrodes electrically connected to the first transistor collectorelectrode and to said second bias means, respectively, for biasing saidsecond and third transistors off during quiescent conditions; and havingcollector electrodes connected in series through said lamp to receivethe one polarity voltages from the power supplies; said first transistorbeing cut off and causing conduction of said second transistor andillumination of said lamp for indicating failure of the associated powersupply when either the relative magnitude of the one polarity voltage,or the relative magnitude of the other polarity voltage, or boththerefrom change in one direction an amount greater than a prescribedlimit; said third transistor conducting and causing illumination of saidlamp for indicating failure of the associated power supply when eitherthe relative magnitude of the one polarity voltage, or the relativemagnitude of the other polarity voltage, or both therefrom change in theother direction an amount greater than a prescribed limit.
 2. Apparatusaccording to claim 1 wherein each alarm circuit includes a pair ofsteering diodes, each diode being connected in series with a differentoutput line of the associated power supply, said first, second and thirdtransistor collector electrodes being connected to the one side of onediode that is spaced from the one output line supplying the one polarityvoltage.
 3. Apparatus according to claim 2 including means responsive tocurrent in the common collector circuits of said second and thirdtransistors for producing an audio indication of failure of a powersupply.
 4. Apparatus according to claim 3 wherein said second bias meanscomprises a resistive voltage divider connected across the supply outputlines and a fourth transistor of the one type having a collectorelectrode electrically connected to the one side of the one diode,having a base electrode electrically connected to the voltage divider,and having an emitter electrode electrically connected to the baseelectrode of said third transistor, said fourth transistor being cut offduring quiescent operation and conducting for causing said thirdtransistor to conduct to illuminate said lamp to indicate failure of theassociated power supply when either the relative magnitude of the onepolarity voltage, or the relative magnitude of the other polarityvoltage, or both therefrom change in the other direction an amountgreater than a prescribed limit.
 5. Apparatus according to claim 4wherein said second bias means includes a zener diode electricallyconnected between said fourth transistor base electrode and the outputline supporting the one polarity voltage from the associated supply forcausing conduction of this transistor when the opposite polarityvoltages therefrom each increase in absolute value more than aprescribed amount at the same rate.
 6. Apparatus according to claim 5wherein each alarm circuit comprises a relay including a coil connectedin series with said second and third transistor collector electrodes andsaid lamp, and said audio indication producing means comprises an audiodevice responsive to operation of said relay for producing an audioindication of failure of a power supply.
 7. Apparatus according to claim5 wherein said audio indication producing means comprises an audiodevice and a relay electrically connected to the sides of said steeringdiOdes away from the supplies and to said audio device, said relay beingnormally energized to deactivate said audio device; and wherein saidalarm circuits each comprise a fifth transistor of the oppositeconduction type electrically connected across said relay and to saidsecond and third transistor collector electrodes, said fifth transistorbeing responsive to conduction of either of said second and thirdtransistors for conducting to short circuit and deenergize said relay toactivate said audio device to produce an audio indication of failure ofa power supply.